Apparatus and method for detecting the rotational movement of a shaft

The invention relates to a device for detecting the movement of rotation of a shaft (3), comprising a flux modulator (5, 15) that rotates with the shaft and through which a magnetic circuit runs, whereby the flux modulator (5, 15) modulates the flux in the magnetic circuit with n number of periods per rotation of said shaft (3). The device also comprises a magnetic field sensor (7) for detecting fluctuations in the magnetic field in the magnetic circuit that are caused by the rotation of the flux modulator (5, 15), in addition to a comparator (23, 24) that compares the output signal of the magnetic field sensor (7) with a threshold value. The comparator (23, 24) emits a signal that indicates a movement of rotation when the output signal of the magnetic field sensor (7) exceeds the threshold value in a given direction. No signal is emitted when the output signal exceeds the threshold value in the opposite direction. The movement of rotation can thus be detected with a certain amount of tolerance with respect to inaccuracies and drifting of said threshold value.